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Check out The Fuel Pulse Show Podcast

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Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

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Check out The Fuel Pulse Show Podcast
Check out The Fuel Pulse Show Podcast

Fuel Testing


The Importance of Fuel Testing As Part of Fuel Preventative Maintenance

Businesses that store fuel - Hospitals & healthcare facilities, backup generator owners, citiy and county services, fire and police stations, utilities, telecom and data centers - they rely on stored fuel to execute the critical emergency backup functions that ensure they can continue doing what they need to do at all times.

Given how important their services may be to their constituents, preserving the health of this stored fuel is of utmost importance. Some groups like healthcare facilities are governed by specific regulations that require them to pay more attention to their stored fuels and emergency generators than other types of users. An example of this might be the AHCA requirement for hospitals to test their backup generators at least once a month for at least 30 minutes. And they may be required to test their stored fuel and file paperwork to show that it’s still in spec.

Not everyone is bound by requirements like these. There are lots of groups out there who either don’t know the importance of fuel testing for the health of their stored fuel or they’re not sure exactly how to proceed. What tests are important for stored fuel and why? What these tests tell you about the health of the fuel.

These are important questions to have good answers to.

We’ve Never Had To Do Fuel Testing Before, So Why Now? Because Fuels Have Changed

If today’s fuels weren’t substantively different from yesterday’s fuels, we probably wouldn’t be having nearly the kind of discussions we are having. The major changes to stored diesel fuel stem from three things: the reduction in sulfur content, changes to the petroleum fuel composition, and growing presence of biodiesel. These changes have made diesel fuel much better for the environmental, but we also have to acknowledge that this important came with a price tag - a concurrent change in the fuel’s ability to resist, or tendency to have, certain kinds of problems.

Ways Diesel Fuel Is Different Than Before

Today’s diesel fuels are significantly more prone to developing microbe problems than stored fuels of decades past. The removal of sulfur and the low caps on aromatic content have created a fuel that burns cleaner, but which has very little resistance to microbial growth (both sulfur and aromatic molecules tend to inhibit microbial growth). Today’s diesel fuels attract and hold more water. They’re also made with cracked petroleum feedstocks that weren’t as common back in the day. 

All of these changes, put together, mean today’s diesel fuels are more prone to filter plugging, corrosion, engine deposit formation, and going unstable in a much shorter period of time than the fuels of yesterday.

Fuel Testing for Stored Fuel Is Important For Whom?

Groups that either store fuel to use it themselves or which serve a customer base that relies heavily on stored fuel and fuel storage tanks. These are groups like state and local municipalities – what we would term government entities. Hospitals and health care facilities. Fuel polishers. Generator users, as well as the generator service companies that provide the service for these users. And plenty of others who use stored fuel. They’re all being impacted by these fuel changes.

Why Fuel Testing Is Important For Government Entities & Municipalities

Government and municipal entities provide the basic services that city or county residents rely on being provided in exchange for their tax revenue. So think of sanitation, water, street and infrastructure maintenance, schools, fire department and police services, even the health department.

They can rely heavily on stored fuel to execute their functions, whether it’s having fleets of service vehicles that pull fuel from fuel storage tanks or a fire station or police station having emergency backup generators to make sure services stay intact during emergencies.

So for them, preserving the health of their stored fuel is critical. If their stored fuel isn’t up to the task of performing, they fail their constituents, and that can be serious trouble. Fuel testing is important for them to help them stay ahead of any shifts in stored fuel condition so they’re not caught offguard at a critical time.

Why Fuel Testing Is Important For Hospitals & Health Care Facilities

Hospitals & healthcare facilities rely on stored fuel to execute the critical emergency backup functions that ensure they can continue giving critical care at all times. We’ve heard the horror stories from Katrina and Superstorm Sandy about when hospital generators fail. And situations like this brings high levels of liability for the institution along with unwanted attention from regulatory agencies.

And speaking of regulatory agencies, given how important these services are to their patients & their customers, preserving the health of this stored fuel is of utmost importance – so much so that many healthcare facilities are governed by specific regulations groups like AHCA that require them to pay more attention to their stored fuels and emergency generators than other types of users might have to.

The AHCA requirement to test backup generators at least once a month for at least 30 minutes, and that fuels must be tested annually to show they meet the full ASTM D-975 requirements. Thus, fuel testing is an essential tool for health care facilities to fulfill what’s required of them.

Why Fuel Testing Is Important For Fuel Polishers

Fuel polishers differ from the previous two groups in that they don’t have stored fuel themselves, but their key service revolves around servicing the fuel of their customers. For their customers, engaging the services of a fuel polisher revolves around both solving of existing problems in their fuel and preserving it for the future so they can continue getting the job done while avoiding nasty surprises.

Since the business of fuel polishing revolves around the servicing of other peoples’ stored fuels, the problems fuel polishers might have in this context are more about the problems of their customers that they get blamed for. Which can very easily impact the credibility of their business, right or wrong.

Where does fuel testing fit into this? It can help them differentiate themselves from the shady operators in the industry because they can prove to their customers that the service did what they said it did.

Why Fuel Testing Is Important For Generator Owners and Service Companies

A fourth market vertical that relies heavily on stored fuel are the backup generator owners and the associated service companies that deal in emergency backup generators. Generator owners can cover a host of other businesses – grocery stores, convention centers, data centers, telecom operations and other business that could be termed as “mission critical” entities. For these groups, keeping up with their generator isn’t their primary business, it’s just a support piece. They’re in the business of selling groceries or keeping the cell phone towers and servers online.

The problems and concerns these generator dealers and service companies have are quite like what we just discussed with fuel polishers. Stored fuels impact their business because its role in making their customers’ generators work as needed, every time. So if there’s a failure, the customers never blame the fuel; they blame the service company or the generator dealer, because it was their product that didn’t work when needed.

Fuel testing is an important tool for both of these groups. It keeps the generator owner apprised of potential problems with the fuel they rely on. And it helps the service company to fulfill the value proposition their customers expect.

When’s The Last Time You Had Your Fuel Tested?

Maybe you’re involved with one of these categories. Just as with storage tanks, you may already be subject to requirements to do fuel testing at given intervals. Hospitals and critical use facilities typically fall under these requirements. For everyone else, the most common practice with stored fuel is a reactive one – if you don’t see problems in the present tense, everything is fine. You’ll deal with problems if you come across them. On the other hand, fuel sampling and testing, even if it’s just once a year, goes a long way in identifying future problems and heading them off. Without fuel testing, you have no sure way of knowing these critical problems exist or may be on the horizon.

What Tests Should I Do?

In order to know what to do, you have to know what’s important to pay attention to. There’s a lot of information out there and it can all start to look like white noise. What are the aspects of the fuel that tell us whether it’s in currently useable condition? What should we look at to tell us how long it’s likely to stay that way?

To have these answers, you need to identify the tests that show both the current condition of the fuel and whether it’s likely to stay that way.

ASTM Fuel Tests – The Gold Standard

There are lots of standardized tests you can consider, but the gold standard are the ASTM tests. They have procedures have been vetted and agreed upon by industry groups – the people who know best. They are reproducible, so that a test that can be done the same way by different people and produce results that can be meaningfully compared. And there are plenty of places you can have them run.

The ASTM Organization

To understand the value and advantage of ASTM testing, the best place to start out at is talking about the ASTM organization itself.

In a nutshell, ASTM’s purpose is to create standards for many of the things we use in everyday life and in business.

ASTM of course is an acronym that stands for American Section of the International Association for Testing Materials. It was originally started in 1898 by a group of scientists and engineers who were working in the railroad industry (Pennsylvania Railroad). There were tremendous problems with rail breaks, so their first job was to develop a standard for the steel used to fabricate the rails.

Now, you would think that having industry standard would be good for business, but it’s interesting to look back and see that, at first, industry was very resistant to the idea of defining standards for things like that. They were afraid that doing this would just cause mass business anarchy - everyone would just default on contracts. But business and industry came around in a big way as they began to see the value in doing this kind of thing. And so here we are today.

Today, ASTM has over 30,000 members from more than 140 countries, and there are more than 140 technical committees. These committees span across all kinds of industries and areas. These committees (i.e. Committee B01 Electric Conductors Committee and the D10 Packaging Committee) are the ones that decide what the standards should be. They’re typically composed of people who have some kind of interest in whatever thing it is they are looking at. This means they can be users of products, producers of products, general consumers, or just people who are interested in the particular thing. But this also means they’re not “interested parties”, it means they’re more likely to be the experts in the specific area – the kind of people you want deciding what tests and standards should look like for a subject.

What ASTM Does and Why Are There So Many Standards?

ASTM’s job, its mission, is to formulate standards for many of the things that we use in life. We said that there were more than 140 technical committees, but there are more than 12,000 ASTM standards that have been created and are adhered to by some significant party.

Why are there so many standards? Think all the things we use and think of the assumptions that you have when you use them. You proceed under the assumption that they are what we think they are, in terms of their properties. You might buy a cardboard box, and you assume that the walls are going to be a certain thickness and it’s going to have given abilities that will reasonably help you do what you want it to do (ship or store something securely). Those properties all have the be defined, or else anyone can just pick whatever they want it to mean.

There are ASTM standards that define and cover most of the things we come across in our business and personal lives:

  • A492 – the standard specification for stainless steel rope wire
  • E112 – the test methods for determining average grain size (in farming)
  • C91 – cement and concrete standards

For almost anything you can think of, there’s at least one ASTM standard that played a key role in ensuring that it was what you thought it was.

Why ASTM is Valuable – The Vetting Process

One big reason why ASTM tests are the gold standard is the process they use for coming up with a given standard? Without going too much into the weeds on this, the basic process would look something like this:

  • Once someone decides on the topic that needs to have a standard developed, they form a Task Group that does leg work and research that forms the basis of a draft standard. 
  • They submit their findings for review and voting, where it is reviewed, discussed and voted on by a series of subcommittees and then the Main Committee. 
  • If it passes muster with all of those, it’s put up for vote by the entire Society, which has to approve it before it can become an official ASTM International Standard.

As you may be able to tell, this process ensures that only fully vetted and agreed-upon standards actually become written into “law”, so to speak. It means the ASTM tests and standard have the full intellectual and practical weight of the people who know the most about the particular area.

Can’t ASTM Test My Fuel?

One other thing to remember is that, although we’re discussing testing here, ASTM itself doesn’t do any actual testing. They determine what group of tests should define a given standard, and what kind of tests results should be the standard for whatever they’re talking about. Then it’s up to testing labs to execute those tests. 

ASTM’s Influence

The ASTM organization is referenced so much, in so many place, you might think it pretty much rules the roost. But with respect to its influence, you have to understand that the ASTM itself has no clout or role in forcing anyone to adhere to whatever standards it comes up with. That clout actually comes when someone else, like the United States government, decides that an ASTM standard for….whatever…..should be the standard or the definition adopted for a given thing. 

When the Federal Government does this, it actually comes from the 1995 National Technology Transfer and Advancement Act that requires the federal government to use privately developed consensus standards whenever possible. So, an example of the United States government giving ASTM some clout is the rule that that all toys sold in the US have to meet safety requirements of ASTM F963. ASTM can’t force toy makers to make safe toys; they just define what safe toys look like. But the government is the one that tells people they have to pay attention to what the ASTM says in that regard.

And that’s the kind of situation we have with a similar requirement for ASTM D975 – the diesel fuel standard. The federal government decided that the D975 set of rules were what best defined the thing called diesel fuel. If you want to legally call something Diesel Fuel, it has to meet the definitions listed in D975. It has to meet all of the particular stipulations contained therein (while also implying that if it’s not contained in D975, it doesn’t have to be so in order to still legally be Diesel Fuel). This last point is also necessary to consider. Let’s say someone wanted to add blue dye to diesel fuel. D975 doesn’t say anything specifically about color defining diesel fuel. It just says fuel has to be “clear and bright and free of visible particulate contamination”. So someone can add blue dye and still legally call it diesel fuel. Of course, that’s a separate issue from whether it’s actually a good idea to do something like that, and there may be other rules that prohibit them from doing that. But those are separate from the ASTM’s specification-based definition of diesel fuel.

What ASTM D975 Tells Us About Diesel Fuel

This discussion of the ASTM and its role should be leading us to make the key connection that fuel testing has an important role. In any discussion of fuel testing, you always start by recognizing that testing the fuel is about answering two questions:

  1. Are the fuel’s properties what they should be, right now?
  2. How likely are the fuel’s properties to change in the future?

So, we always focus first on the fuel specifications - the descriptions of properties of the fuel that relate to important areas of its functionality. We always start with the ASTM D75 document. It’s what defines the minimum set standards for what diesel “fuel oil” should be.

ASTM D975 tells us that an ideal diesel fuel is one which flows easily at all temperatures, is clean and free from foreign contaminants and separated wax, ignites readily and burns quietly, cleanly and economically. These descriptive ideals are reflected in the diesel fuel’s specifications.

The ASTM Diesel Fuel Specifications: Combustion vs. Non-Combustion Properties

Every fuel specification is important because it contributes to the fuel behaving in a desirable way. If a fuel does not meet a given specification, that’s when you may see symptoms of a problem in how that fuel is behaving, whether in combustion system you’re using it in or in the storage and distribution system it lives in.

So let’s run through the list of diesel fuel specifications - what they mean, how they’re measured, and what you’re likely to see happen if a diesel fuel does not meet that particular specification. What are these properties that diesel fuel has to meet minimum standards on? Many of these are specifications you may have heard referenced in other areas. As we go through them, we’ll start to see how these properties really are important for making sure diesel fuel does what we need it to do.

Diesel fuel specifications (and specs for gasoline, too) can be divided into two classes: ones that influence combustion, and all the rest of them. First, the combustion-related specifications.


ASTM number / Is it in the D-975 slate?

Minimum value

What Is It/How is it measured?

What happens if the fuel fails?







Density is the weight of a unit of volume, typically measures by a hydrometer.

Density is linked to the heating value of the fuel.

Higher density fuel produces more smoke but more power (because it has more energy value per unit of volume).

DENSITY - The very first one we look at isn’t technically defined in the ASTM standard. So maybe you’re wondering why include this? Density is an essential property of diesel fuel, but it’s not defined by an ASTM test because it’s actually governed by the results of other standards that we’ll see later, like Distillation and Aromaticity and Cetane Number.  If those tests are within spec, it means the density will be within ideal range, too. 

Volatility (Distillation)


282-338 deg C for 90% recovery

Volatility is expressed in terms of the temperature at which successive portions (%s) are distilled from a sample of fuel under controlled heat.  Values are usually determined for 10% and 90% recovery, as well as initial boiling point.

Distillation or boiling range influences other properties like viscosity, flash point and density.



Fuel refineries can try to hit distillation ranges by altering the amounts of low or high temp components blended into the fuel.

Raising the back end (90%) temperature will raise the cloud point.  Lowering the front end (10% or IBP) temperature lowers the flash point and raises the vapor pressure, which can result in vapor lock.

The 10% recovery temperature reflects how well the fuel will start to vaporize. 

The 90% recovery indicates the extent to which complete vaporization of the fuel may be expected  in the combustion zone. 

Excessive high boiling components leads to engine deposits and more smoke. 

Diesel fuel with unsatisfactory distillation temperatures may be contaminated with other compounds like gasoline. 

DISTILLATION – this has both physical distillation and simulated distillation (a shorter version of the test). They heat the liquid up until it turns into a vapor, where it will rise up in a column and start to cool. As it cools, it turns back into a liquid and is collected. Distillation tests are looking for the temperature at which 90% of the original liquid volume is condensed back and collected. 

To meet the standard, No. 2 diesel distillation temperature can be between 282 and 338 deg C.

Distillation temperature matters for a couple reasons:

  • It speaks to whether the diesel fuel is going to combust as fully as needed within the typical conditions of a compression ignition engine. If the temperature is too low or too high, it may not fully combust or it may burn too quickly or too early.
  • ·Distillation temperature is actually related to some of the other properties of the fuel, like Cetane Value and % Aromatics.  Keeping the distillation temperature within the required range helps ensure that the diesel fuel has the right composition of molecules in it, like the ratio of light end components vs heavy ends. 



1.9 – 4.1 mm2/S

Viscosity is resistance to flow. Higher viscosity means greater resistance and slower flower.

Viscosity is measured with an apparatus that measures the amount of time needed for a fixed amount of liquid to flow through a capillary tube viscometer immersed in a temperature-controlled bath.

Fuel with viscosity that falls outside the specified range cannot be properly metered/injected into the combustion chamber.

Changes in viscosity will alter the injector spray penetration rate, the cone angle and the droplet size distribution.

If the fuel atomization is subpar, as such, you won’t get optimal mileage and performance and you’ll have higher emissions.

Excessively high viscosity makes fuel difficult to flow in cold temperatures. 

KINEMATIC VISCOSITY – we’re all at least somewhat familiar with the concept of viscosity – the expression of internal friction of a liquid. Thick liquids like honey have high viscosity values, thin liquids like water have low values.  No. 2 diesel has to have a viscosity between 1.9 and 4.1 mm2/S.  The question might be asked, why does viscosity matter for diesel fuel? Because viscosity affects how the fuel can be injected by the injectors (which can affect other things like emissions and engine performance). 

Cetane number (index)




Index is a calculated value derived from fuel density and volatility (distillation). Illustrates the readiness of a fuel to ignite when injected into a diesel engine. 

Cetane number itself is calculated using a specialized engine, which is more expensive.  Test results are compared to the index values of a high and low cetane reference fuel, and results calculated from that.


Diesel fuel with poor cetane number/index will have poor ignition quality. You’ll have less power, noisier and rougher running engine. 

Also linked to cold starting difficulties.

CETANE NUMBER – we’re familiar with the importance of cetane in diesel fuel. And 40 is the minimum value defined by the regulation in the United States.  What we can also see in D975 is that there is an additional requirement that says, you either must have a Cetane Index test that also meets a 40 minimum or an Aromatic content test that has a maximum of 35%.

Flash Point



38 deg C for #1

52 deg C for #2


Temperature at which the fuel has to be heated to produce a vapor/air mixture that will ignite when a flame is applied.

Flash point relates to front-end volatility of the fuel. Refineries have to choose the right light refinery streams to be included in the fuel blend so that the IBP remains sufficiently high enough.

For Pensky-Martens, a fuel sample is heated slowly in a covered cup at a constant rate. At regular intervals the cover is opened and a flame is introduced.  The procedure is continued until the fuel temperature is high enough for flash ignition to occur.

Low flash point influences safe handling of the fuel.

Has no significance on performance in a diesel engine. Variations in flash point will not influence autoignition temperature.

FLASH POINT – the minimum temperature at which something will ignite in the presence of a flame or ignition source.  This is different from autoignition temperature, a high temperature that speaks to how hot something has to be to self-ignite without any ignition source.  Flash point matters because of how diesel fuel works in a compression ignition engine.  If the flash point is too low, as in gasoline (which has flash point of -45 deg F), it will prematurely ignite and damage the engine.



35% max.

Many times, it is calculated using an equation that factors in density and viscosity.


Affects emissions (NEED MORE INFO).

Aromatic content also inhibits microbial growth, so putting a cap on aromatic content makes the stored fuel more likely to support microbial growth.

AROMATICITY (the fuel’s aromatics content) can affect the distillation curve temperature, can produce harmful emissions, and can produce excessive ash. So you don’t want too high a content of them.  They also inhibit microbial growth, which means limiting aromatics to make the fuel “greener” makes it more likely to have microbial growth problems.

Now, the other important specifications that don’t directly influence combustion.


ASTM number / Is it in the D-975 slate?

Minimum value

What Is It/How is it measured?

What happens if the fuel fails?

Cloud point or CFPP







D2500 or 4539/YES

There are no stated values in the D975 spec.

Cloud point = temperature below which wax crystals will precipitate out of the fuel, giving a cloudy appearance.

CFPP is the predictive temperature at which enough wax comes out of suspension that it blocks fuel filters and shuts down engine operation.

We know what this answer is.

COLD FLOW OPERABILITY REQUIREMENTS – D975 mentions both Cloud Point temperature and CFPP (cold filter plug point). But what’s interesting is they don’t give required values for those. In note J, they say “it’s not realistic to require minimum temperatures for fuel because they’re so variable”. The specification only gives guidelines, but not requirements. 

Oxidative stability



2-3 mg/ML is typical

This measures the stability of the fuel i.e. ability to resist sediment formation when subjected to accelerate oxidative stresses. 

A sample of fuel is eated to 95 deg C and maintained for 16 hours in the presence of continuous oxygen.  Fuel is then cooled and solvent washed to recover gummy residues that may have formed.

They may also measure the color of the fuel before and after using the D1500 test described below.

There’s also the D4625 test which takes 100 days (fuel held at 43 deg C) and is believed to correlate with ambient storage conditions for one year of storage. However, this takes too long to be  used for routine quality control at the refinery level.

Excessive gum formation predicts lack of storage stability of the fuel.

Fuel instability is responsible for numerous phenomenon, including deposit format in injectors and combustion chambers, as well as subpar emissions products and engine operation.

Thermal stability



F-21 DuPont

70% is the satisfactory cutoff


This is used to predict how well a fuel will resist sediment formation upon longterm exposure to higher temperatures.

Two 50ml fuel samples are heated to 150 degrees and held for 90-180 minutes with oxygen exposure. Fuel is then cooled and filtered.  The filter pads are then exposed to light to measure their reflectance.  Higher amounts of filtered insoluble yields a lower reflectance score, expressed as a % reflectance.

Reflectance scores of 71+ are considered good.  62-70 is “fair”.  Below 70 is marginal or worse.

The color of the fuel sample can also be logged before+after using the D1500 color comparison test. Typically, an aged fuel sample will end up with a higher (darker) color score.


Higher levels of filterable insoluble predicts fuel that is more likely to form gums and deposits in storage over time.

These are essential tests for predicting whether stored fuel will stay in viable condition or not. We’ll discuss the importance of this later.

Water and sediment





.05% vol, max.

Water comes from any number of points in the distribution system.  Sediment content can be from inorganic deposits (rust in bottom of the tank) or organic deposits (degradation of fuel, bacterial action, wax settling that does not dissolve).

A 500ml sample of fuel is mixed with 500ml of water-saturated solvent in each of two graduated tubes.  Samples are centrifuged to concentrate the water and sediment at the bottom of the tube.

The sum is reported as the % of water and sediment.

Excessive water content can encourage growth of microbes and may block filters.

Excessive sediment content may be a sign of fuel instability and can cause wear in injectors.

Corrosion and wear in the engine and fuel injection system.

WATER AND SEDIMENT CONTENT is defined in D975 and relates to the amount of contamination present in the fuel.  It’s also been strongly linked to the presence of microbially-induced corrosion (MIC) present in storage tanks. So it’s an important test to pay attention to. 

Ash Content



.01% mass, max.

Small sample of fuel is burned in a weighed dish until all combustible material has been consumed. The unburnt residue is weighed and reported as a percentage of the original fuel sample.


All diesel fuel contains small amounts of ash-forming material like suspended solids and soluble organometallic compounds.

These can cause damage in the close tolerances of fuel injection equipment.

Contibute to increased deposit levels and abrasive wear of piston rings and other components in the high temperature zones of the engine (where the fuel gets burned). 

ASH CONTENT – on the face of it, this one seems pretty important.  You want the fuel to burn cleanly and completely, without producing leftover ash which can damage areas of the engine.  Ash itself comes from a combination of partially-burned carbon components (like aromatics) and inorganics (like metal content).  Obviously you don’t want much of that if you’re burning diesel fuel in, say, a truck engine. 

Ramsbottom Carbon residue



0.15% max for Kerosene #1

0.35% max for #2 diesel

Test measures the amount of higher bp, lower volatility components are present in the finished fuel (some entrainment of higher bp materials occurs during refinery distillation).

Carbon residue in diesel is already low, so the test is run on the 10% residue from the laboratory distillation test to improve accuracy.

A 4g sample of 10% bottoms is placed in a glass cooking bulb and heated at 550 deg C for 20 minutes. After cooling, the bulb is reweighed to determine amount of residue.

Carbon residue test indicates the tendency of the fuel to form carbon deposits, although it does not predict injector coking.


RAMSBOTTOM CARBON RESIDUE – This is a measurement of the residue the fuel is going to produce at high temperatures, such as those you might find in a diesel engine. As with ash content,  you don’t want a lot of that.  A high score on this means you’re probably going to have combustion chamber deposits formed.















Differs by country.  Italy has a minimum of 2.5.  France has a max of 5.0.

Sample of fuel is placed in a jar and examined under a standard light source.  Colored glass discs are used to assign a numeric value for the fuel’s color. Range goes from 0.5 (pale) to 8.0 (darkest).

Dark color may indicate the presence of heavy cracked gas oil and residues (acts as a safeguard to ensure no monkey business).  Dark color can also hint at fuel instability, as the color spec. is part of the Thermal Stability test.




520 microns

Also refers to film strength, is the ability for the liquid to lubricate essential moving parts in the engine.

Measured on an HFRR machine, which wears the size of a wear scar left behind by steel balls immersed in the liquid and subjected to measured pressure for a defined period of time.

Unsatisfactory lubricity can predict the inability of the fuel to protect injectors and fuel pumps from premature wear.

Fortunately, the addition of low-level biodiesel to diesel fuel has solved the lubricity problem.

LUBRICITY – All of these diesel fuels are capped at an HFRR score of 520, in other words, they want to be lower than that. 

Sulfur Content








15 ppm for ULSD




Sulfur content is controlled by regulations to help the environment.

Typically measured by some kind of mass spectrometer, which can detect the weight % content of sulfur.

Excessive sulfur in the fuel can poison the emissions catalyst. It can also lead to big regulatory fines if detected.

SULFUR CONTENT – we are all well familiar with the sulfur issue, and Do975 is one of the places that spells out the requirements. 15 ppm for the S15 diesel fuels, 0.05% (which is 500 ppm) and 0.50% (5000 ppm) for the S500 and S5000 diesel fuel oils.

Copper strip corrosion



No. 3.

A score of 1-3 indicates tarnish but is permitted. A score of 4 indicates corrosion and is not permitted.


A polished copper strip is immersed in a portion of fuel and heated for 3 hours at 50 deg C.  It is removed, washed and compared with an ASTM standard chart.

Copper is used because copper and its alloys are sensitive to attack by certain sulfur compounds, so they are a good indicator. 

A failing grade on this test implies that the fuel is excessively corrosive and may attack metals in the fuel distribution and storage network.

COPPER STRIP CORROSION – this tries to verify that the diesel fuel isn’t going to cause corrosion damage by long-term contract with metal parts. The test itself is run by taking a strip of copper metal and immersing it in test liquid for a define period of time and temperature.  The strip is then compared to a visual chart and given a grade.  

The Essential ASTM D-975 Tests For Stored Fuel

This is the important stuff. Having seen the importance of the diesel fuel specifications and what they tell us about the fuel and its performance, we should consider the most important tests that stored fuel users should run. And we start off with the most important ASTM tests that are listed in the D975 specification list. 

Test #1 – Water and Sediment Content (ASTM D-2709)

The D-2709 test measures something very important – the amount of water and sediment in the sample tested. The test is run by taking a fuel sample and centrifuging it to force any water and sediment that’s in the fuel sample to the bottom of the tube. They then measure what was pushed to the bottom to give a volumetric content measurement.

One thing to remember about this test is that it’s a test that tells you what the actual sediment and water content is in the fuel. It’s descriptive – what is the fuel like RIGHT NOW. This makes it different from some other tests we may talk about later which are PREDICTIVE tests, like stability tests.

Water and Sediment Content: What Can It Tell You?

Excess water presence is a key supporter of microbial growth in fuel and storage tanks, while failing readings on water and sediment content are strongly correlated to existing storage tank corrosion because of its contribution to likelihood of microbial growth. Water and sediment content also have strong links to issue of poor engine performance or possible mission critical equipment failure, a critical issue for anyone who relies on the stored fuel to work in an emergency.

For service entities and their customers - fuel polishers and generator service companies – the Water and Sediment Content test is very useful to document how the fuel has improved from before to after service. Customers get peace of mind and the service companies gain increased legitimacy that they did what they said they would.

Water and Sediment Content – What To Do If Fuel Fails This Test?

The only way to fix a poor result on this test is to have the water and sediment removed. This implies the need for some kind of fuel polishing or fuel cleaning. So this is good news for the fuel polishing market vertical. The Water and Sediment test shows the need for their services.

Good fuel polishers will utilize a combination of fuel filtration, tank cleaning, and good chemical treatment of the fuel. It’s important to implement a complete solution here. Filtration and fuel polishing removes the water and sediment, which brings the fuel back into spec if you were to retest the fuel.

But this alone doesn’t really do anything about keeping the problem from coming back. A good fuel polisher or service company who follow best practices will also incorporate quality chemical fuel treatments – fuel stabilizers and biocides at a minimum, which will help keep this reading in spec for as long as possible.

Test #2: Cetane Index (ASTM D-4737)

A couple of things that remember with this one. The first thing we should point out is Cetane Index is not to be confused with the Cetane Number test (D-617). Both of these tell you the same thing – they measure or estimate the cetane rating of a diesel fuel sample. And this is important because it provides a picture of the combustion quality of that fuel.

Cetane Index vs. Cetane Number are run in different ways. Cetane Index is a calculation that takes the results of a couple of other tests - Distillation and Density measurements - and calculates an estimation of cetane rating from those results. It’s simple, fast, and accurate enough that it’s considered a legally viable substitute for Cetane Number (which is more expensive and harder to run).

It’s important to note that Cetane index does not account for the addition of cetane improver additives. Which means you can use it to establish if you need to improve the fuel cetane rating, but you wouldn’t use it to measure what the change was after you did it..

Cetane Index: What Can It Tell You?

The problems with a subpar cetane rating stem from combustion deficiencies that would happen in the engine. Poor starting and rough operation, for both stationary and vehicular engines. More black smoke because fuel with subpar cetane rating is less likely to combustion as fully as it should, given that it’s detonating too quickly, relative to where the piston is in its cycle. And if the cetane rating is low enough, the fuel may not support sustained engine operation at all.

These are all troubling implications for anyone has a mission critical or emergency backup engine, that needs to fire that engine or machine up in an emergency and have it work as they need it to. And it has implications for the service providers as well. At the conclusion of service, the customer expects their fuel to be like new and ready for anything. But if the fuel’s cetane rating was poor and nothing was done about it, that fuel isn’t going to work as it should, and the fuel polisher or the generator service company is going to hear about it.

Cetane Index – What To Do With A Failing Test?

This cetane rating problem is a little unique in that a low rating can’t be remedied by the removal of something, like the Water/Sediment test implies. Instead, the remedy is to add a chemical cetane improver to the fuel that raises the fuel’s cetane rating. These cetane improver additives makes diesel engines easier to start and run more smoothly. They improve efficiency, reduce black smoke emissions. And they eliminate the doubt as to whether a limited use mission critical engine is going to perform when it is needed.

Exactly how much you’d need to use depends on the specific properties of the fuel. A reliable and trusted partner should be able to make a recommendation for you. 

What kinds of tests should be considered that are not ASTM D-975

In addition to these D975 tests above, there are other essential fuel tests that should be considered for stored fuel. Some of them have ASTM numbers associated with them (but may not be spec’d in D975), while others do not (but are still important to consider).

Test #1: Microbial Presence

Microbial Presence/Count

What is this test? How do you run it?

What problems can it predict or detect?

What to do if your fuel fails?

Multiple test options, ranging from simple and quick to more rigorous.

Cultured test strips are easy to use and give a qualitative (yes/no) indication of the presence of microbes in a sample. 

“Fuel Stat” test kits give a immediate and semi-quantitative reading of specific kinds of microbes that may be present in the fuel and water bottoms.

ATP tests also indicate not just the presence of microbes but how many.

Microbial Count testing is done by submitting fuel samples to a certified lab and uses phase contrast microscopy and a machine like a Coulter Counter to mechanically count the number of microbial bodies within that pass through a scanner.

TANK CORROSION from strong and weak acids produced by microbes in the storage tank.

FUEL DEGRADATION from being consumed by microbes during their life cycle.

BIOMASS FORMATION, FILTER PLUGGING DEPOSIT FORMATION which are, at the least, a hassle, and at worst, can be a major cause of both waste time & resources and lost engine performance.

EMERGENCY EQUIPMENT FAILURE from the reduction in fuel ignition and combustion quality. Additionally, the “out of sight, out of mind” nature of storage tank contamination coincides with the purpose of emergency/backup equipment – a health care facility can’t predict exactly when they’ll be called on for use in a critical situation.

Application of biocide to the fuel in the storage tank is the only way to effectively reduce microbial counts in fuel.

Mechanical fuel processing to remove biomass and dead microbial presence after biocide application.  This will reduce future filter plugging and remove some of the existing precursors for future fuel instability.

Use of biomass dispersants & anti-corrosion treatments to help remove biomass and microbial presence from storage tank surfaces and prevent re-inoculation of the fuel supply.


Microbial Presence/Count testing is vital to keeping on top of the most damaging single element in the universe of fuel storage. Regular monitoring of microbial counts is a best practice for health care facilities to enable sound decision making on how and when to utilize biocide treatment in the course of ensuring their stored emergency fuel stays sound.

Microbial Presence Tests – Next-Gen ATP Technology Leads The Way

Microbial presence in stored fuel that serves any kind of critical function is not something you want to mess around with, especially since diesel fuels have changed in the ways they have.

It used to be that the only options for confirming a microbial problem was to send fuel samples off to a lab and wait up to 28 days for culture results to come back.  Those days are behind us. It’s becoming easier for fuels managers to include microbial monitoring in their regular fuel housekeeping.

For in-field tests, there are three main types of options. All of them involve pulling a fuel or water sample from the tank and applying it to a test medium.

CULTURE STRIPS might also be called Dip Slides.  They’re the simplest of the bunch, you dip the strip in fuel, put them in a safe place and wait 3-5 days.  They can be used as a rough indicator of a microbe problem because they are mainly qualitative: yes or no. Although there are some test strips that have a very rough quantitative aspect to them, and some will differentiate between classes of microbes – bacteria vs. mold vs. fungus vs. other kinds of organisms.

The cost for these tests can range between $5-10 a test, so not that expensive.

INDICATOR tests are the next step up (FuelStat, MicrobeMonitor, LiquiCult). They are also indicator tests, they give you a +/- indication, and they can distinguish between bacteria and mold and fungus. The biggest advantage with them is that they give you fast results, within a few minutes, so you can use them out in the field and make decisions on the fly.

The downside to them is two fold – they aren’t quantitative, and they can tend to be pretty expensive, around $100-150 a test.  Depending on your situation, that expense could still be justified, but still that is kind of high for many users

ATP TESTS are newer technology that detects presence and amount of microbial ATP in a sample.  These also give fast results within a few minutes, so they give you an answer in the field. In contrast to FuelStat, they give you a total reading of microbial presence, they do not distinguish between different kinds. 

But on the flip side, they give you a very accurate quantitative measurement, which makes them extremely useful for monitoring both ongoing and situational microbial levels.  And they are also fairly inexpensive. You have an initial outlay for a luminometer that may cost $3000 or so, although you can rent-to-own them from some companies for significantly less. But the bigger advantage here is that the individual test materials only cost around $10-$15 a test. 

The combination of fast action, low cost and an accurate microbe count means fuel managers can actually baseline and monitor their fuel condition and see microbe problems coming before they get serious.  How valuable is that?

Microbial Presence Testing: What Can It Tell You?

If it’s indicated there is microbial presence, the next question is what problems might be inferred?

As with water presence, microbial presence is problematic for virtually everyone, no matter if you’re involved in hospitals, a generator user, service work, or using stored fuels in a govt. capacity.

TANK CORROSION – from the strong and weak acids produced by microbes. And you can get corrosion damage both above and below the fuel line.

FUEL DEGRADATION – because microbes consume and break down elements of the fuel, reducing its storage viability.

BIOMASS FORMATION AND FILTER PLUGGING – because microbes produce organic biomass substances that plug up filters and stick to tank surfaces. At the least, they’re a hassle, but at worst, they can be a cause of wasted time and resources (if you have bad filter plugging problems), not to mention subpar engine performance.

EMERGENCY EQUIPMENT FAILURE –If the fuel quality has been destroyed and there are deposits and biomass contaminating the fuel, it places real doubts on whether the emergency equipment can properly function on-demand, using that fuel.

This last one is the really big one. It’s the one that many of these entities fear the most. Not having the confidence that they can do what they need to do whenever they need to.

Microbial Presence: The Implications Of A Positive Test

In terms of the implications of microbial presence, critical groups like Government entities and hospitals worry about this a lot.  Both of them must be able to provide services to their constituents no matter what.  In the case of hospitals, it’s so important, they are required to keep their fuel in spec by yearly testing, according to ACHA regulations.

Yet, these AHCA regulations don’t specifically require a microbial presence test. All they require is what’s on the D-975 regulation.  And this could be a problem because if microbes get involved, the problem becomes a lot more difficult and serious to take care of. Without microbial presence testing, it’s impossible to know when this point is.

For generator users, they have the same kind of concerns about reliability because many of these generators have a mission-critical function. 

Fuel polishers and generator service companies are also at risk of the effects of the microbes causing huge problems that they potentially can get blamed for.

Microbe problems have serious implications for all of these and more. But all this being said, there is good news for them.  There are a range of in-field options that cost-effectively give both stored fuel users and their service providers the ability to solve microbe problems effectively.

Microbial Presence: What To Do (What Are The Options)?

What are the recommendations for before and after a failing microbe presence test?

Recommendation number one is to change your PM practice (or have your service provider do it) to add regular monitoring of microbial levels in tanks.  And use the relevant test guidelines to help you know when you need to take action.

Once a problem is detected, there are some clear best practice options.

Biocide Application – The Only Way To Really Kill A Microbe Problem

Most important is biocide application. Thi,s of course, is after you remove an free water phase, which is assumed you would do that anyway.

Application of biocide to the fuel in the storage tank is the only way to effectively reduce microbial counts in fuel. This is beneficial both for the user (who gets their problem solved) and the polisher or service provider (because the need for future re-service is reduced. No service provider likes to have to come out multiple times to solve a problem).

Just be sure to use a biocide and not a biostat. Plenty of things like water controllers claim to impact microbes without actually killing them. Stay away from those. A biocide is the only thing that will kill and get rid of a microbe problem.

Once you treat with biocide, it’s recommended to use ATP microbe testing to confirm that what you did worked.  That’s another advantage of quantitative ATP testing over lesser-quality indicator tests.

Fuel Filtering – A Necessary Step After Killing Microbes

Beyond biocide application, you’re also going to need to have the fuel filtered or polished. This will remove the dead microbes (they have to go somewhere), plus any microbial biomass left in the tank.

It’s important to do this because otherwise, you’re going to have filter plugging problems.  Plus it gives an added bonus of removing some of the existing precursors for future fuel instability, which gives you stability benefits.

Biomass Dispersants and Anti-Corrosion Treatments For Added Benefits

A final recommendation is that you consider using both a biomass dispersant and an anti-corrosion treatment in your stored fuel. 

It’s really important to stay on top of the microbial issues, especially if your top priority is having the fuel available for emergencies.

Test #2: Water Content Measure

Water Presence & Content (Stick Test | Karl Fischer)

What is this test? How do you run it?

What problems can it predict or detect?

What to do if your fuel fails?

There are multiple methods for determining water content in fuel, both in-field testing and lab tests. 

In the field, presence of free water (i.e. a tank water bottom layer) can be confirmed and measured through the use of water finding paste (“tank sticking”). 

For a more qualitative measurement, the Karl Fischer lab test gives a qualitative measurement of water content as a percentage of the fuel.

TANK CORROSION: Water content contributes to tank corrosion through multiple chemistry avenues. 

MICROBIAL GROWTH: Water provides an essential medium for microbial growth in stored fuel.

FUEL DAMAGE IN STORED GASOLINE: Increases the risk of phase separation in stored ethanol-blended gasoline, which can quickly destroy the fuel’s viability. 

EQUIPMENT DAMAGE: Excessive water content may also damage fuel injectors and cause problems with common rail diesel engines

Excessive free water should be mechanical removed (pumped out or drained).

Consider incorporating the use of water scavenging fuel treatments to remove trace remnants of water in the storage tank.

Excessive dissolved or entrained water can be treated with a demulsifier chemical to make the water drop out of the fuel, enabling it to be removed by mechanical means.

If excessive free water (> 0.25 inches by stick method) can found, consider modifying your tank monitoring procedures to regularly check for water presence at least monthly.  Tank should always be checked manually – do not rely solely on in-tank water monitoring equipment. Always verify by another method.

Testing for Water Presence is an essential element of proper stored fuel and tank maintenance.  Even though water/sediment content is required by D-975, checking for water manually at regular intervals is easy to do and can head off many problems.

The third fuel test that stored fuel users should be familiar with is a Water Content test.  But we already talked about Water and Sediment. Why are we seemingly duplicating that?

Truth is, we’re not duplicating it. The Water and Sediment test looks at total free water and sediment content in fuel together. This kind of Water Content tests we’re considering here can look at multiple kinds of water content, whether free or emulsified or even dissolved.  Our recommendation would be to consider a couple different Water tests. One can be done in-field, one done in a lab.

In the field, presence of free water (i.e. a tank water bottom layer) can be confirmed and measured through the use of water finding paste (“tank sticking”). This is a basic housekeeping recommendation for anyone who has stored fuel. But while it is easy to do, it only detects free water. You can also do what they call a Crackle test, which detects all 3 kinds of water and has been used in the field for years.

Beyond these the other side of the coin is a qualitative lab measurement called the Karl Fischer titration method.  Some of you might have heard of this – it’s the most widely used water detection lab test. This lab test gives a qualitative measurement of water content as a percentage of the fuel and is highly accurate down to 5 ppm.  If you needed the most definitive answer to how much water is really in your fuel, this is the test you would run. 

Water Content Testing  – What Can It Tell You? 

We have already discussed that the problems with having water in fuel and storage tanks is as much to do about being an essential contributing factor to other primary causes of problems as it is about being a primary problem itself.

TANK CORROSION: Water content contributes to tank corrosion through multiple chemistry avenues.

MICROBIAL GROWTH: Water provides an essential medium for microbial growth in stored fuel.

FUEL DAMAGE IN STORED GASOLINE: Increases the risk of phase separation in stored ethanol-blended gasoline, which can quickly destroy the fuel’s viability. 

EQUIPMENT DAMAGE: Excessive water content may also damage fuel injectors and cause problems with common rail diesel engines

Transition: In view of all this, what we can say is that monitoring of water content is a really high value diagnostic proposition for all of these verticals, because of how many serious problems water content contributes to.

Water Content – What Should You Do?

Once water content is detected, it’s actually not that hard to remediate. You have several options. Excessive free water should be mechanically removed (pumped out or drained) from the storage tank. You can also incorporate the use of water scavenging fuel treatments afterwards to remove trace remnants of water in the tank.

Also, excessive dissolved or entrained water in the fuel can be treated with a demulsifier chemical to make the water drop out of the fuel, enabling it to be removed by mechanical means. This is becoming more and more best practice because of the proliferation of common rail diesel engines and diesels using high pressure injection systems, which have very little tolerance for water.

Virtually all fuel polishing services aim to remove of water from the fuel through filtration.  You can use a Karl Fischer or Water & Sediment test to verify how well the fuel service worked.

Water monitoring should be a regular part of fuel monitoring of anyone who has significant amount of stored fuel. Doesn’t matter if you’re a hospital or a telecom company or a government agency. Keeping on top of water buildup in stored fuel tanks will head off a lot of headaches in the future.

Test #3: Fuel/Water pH Level 

pH Level

What is this test? How do you run it?

What problems can it predict or detect?

What to do if your fuel fails?

Measures the acid/base level of a fuel sample and/or water bottom samples from the tank.

0 is acid whereas 14 is base(ic).  On the pH scale of 0 – 14.0, 7.0 is neutral, while healthy fuel will almost always fall between 5.6 and 8.

The pH scale is logarithmic, meaning each increment of value going toward the acid end of 0.0 increases in size. Therefore, there’s a much greater difference in going from, say, a 2.1 pH to a 2.0 compared to going from a 5.1 to a 5.0 pH.  Use a pH meter to check it.

MICROBIAL GROWTH: Low pH (acidic) readings below 5.6 may indicate accelerated microbial growth in the fuel, as microbes produce acidic byproducts that lower fuel pH.

TANK CORROSION: The presence of acids in fuel and water bottoms

FUEL DEGRADATION: High acid levels in stored fuel are responsible for accelerating the rate of degradation of the fuel. They also contribute to tank corrosion and damage.

Consistently acidic pH readings, when taken as part of a monitoring program, should be an indicator that additional action needs to be taken to head off potential problems. 

Removal of water bottoms and treatment of the tank with biocide to kill microbes that created the acidic environment. 

Highly acidic fuel itself may need to be disposed of, unless it is diluted with fresh fuel before use.


PH level of fuel can be a concern for health care fuels stored long-term for use in critical or emergency situations. It can be a warning sign for the health care facility that they need to look more closely at the conditions in their fuel storage tank, especially if the storage tank holds fuel needed to execute emergency services.

Test #4: Fuel Stability 

Fuel Stability (ASTM D-2274)

What is this test? How do you run it?

What problems can it predict or detect?

What to do if your fuel fails?

Also known as Oxidative or Accelerated Stability.

Measures the storage stability of fuel.

Fuel sample is heated and exposed to oxygen to simulate the process of fuel oxidation that occurs in real life storage.  Insolubles like sludge are produced in the process and measured at the end of the test. 

FUEL INSTABILITY: The Fuel Stability test predicts upcoming fuel instability because unstable fuel produce higher quantities of measurable insolubles.

REDUCED COMBUSTION PROPERTIES: Unstable fuel with high level of insoluble do not combust as freely or cleanly as fresh, stable fuel does.

INJECTOR AND EQUIPMENT DEPOSITS, LEADING TO PERFORMANCE ISSUES AND ELEVATED BLACK SMOKE EMISSIONS: Unstable fuel predicted by the D-2274 test will darken and stratify in storage at a faster rate, producing sludge and reducing combustion viability.  These heavy fuel elements form performance-robbing deposits in injectors and engine areas.  They also produce elevated levels of black smoke emissions.  

PERFORMANCE UNCERTAINTY FOR CRITICAL EQUIPMENT: Fuels that are severely unstable may not be able to sustain proper engine operation, which may be disasterous for a hospital providing essential/emergency services.

Fuel should be polished or cleaned to remove existing insoluble and sludge. 

Fuel should then be chemically treated with a stabilizer to halt further degradation and extend its effective storage life.


Fuel Stability is an essential test to run because it gives a direct predictive indicator of a stored fuel’s ability to withstand degradation over time. This is essential information for hospitals and health care facilities that use stored fuel, if they want to minimize unexpected problems.  Tabulating fuel stability data gives them a useful running picture of the state of their stored fuel.

Fuel Stability (D-2274)

This is perhaps the second-most important test, that of Fuel Stability.  These tests measure the ability of the fuel to resist changes to its composition over time.  This is usually what’s referred to as storage stability.  When you leave the fuel in a storage tank, under ambient conditions, exposed to things like heat and oxygen, will the fuel stay in its original state or will it react and oxidize and stratify and form harmful solids?  How quickly will this happen?  It’s important to know what to expect.

There are at least a couple of tests that measure stability.  One kind is a Thermal Stability test, which predicts changes to the fuel as it is exposed to elevated levels of heat (this makes sense b/c heat speeds up chemical reactions).

The other kind of stability test is the one we’re recommending here - the D-2274 test known as Oxidative or Accelerated Stability.  This test doesn’t focus so much on stability at higher heat as it does fuel stability during exposure to oxygen, which is basically what you’re getting out in the real world. For this test, a fuel sample is heated and exposed to oxygen to simulate the process of fuel oxidation that occurs in real life storage.  Insolubles like sludge are rapidly produced in the process and measured at the end of the test. 

It’s important to remember that Fuel Stability testing is predictive – the results predict the fuel’s condition at some point in the future. So a Stability Test differs from a Water & Sediment test in the Water & Sediment tells you the amount of sediment actually present in the fuel at the time of testing, whereas the Accelerated Stability test infers what happens in the fuel when it is exposed to oxygen over a period of time. 

Fuel Stability Testing – What Does It Tell You?

From this Stability test, you get a predictive score illustrating the state of the fuel in your storage tank. For scores that are subpar, what kind of problems does that infer could be on the horizon?

Well, the answer is…..most of the same kinds of problems that users would see if they had high sediment levels in their stored fuel. You’re talking about problems like:

REDUCED COMBUSTION PROPERTIES: Unstable fuel with high level of insolubles do not combust as freely or cleanly as fresh, stable fuel does.


PERFORMANCE UNCERTAINTY FOR CRITICAL EQUIPMENT: Fuels that are severely unstable may not be able to sustain proper engine operation, which may be disastrous for government entity providing essential/emergency services, backup generator users, ad definitely Mission critical systems using that stored fuel in an emergency.

And lastly, of course, the results of the Stability test can be used to shed light on

POLISHING SERVICE EFFICACY: We mentioned this earlier in the discussion on the Water and Sediment test.  Stabiliy testing is valuable for both the service provider and the customer. If you can do a polishing service and show how the stability rating changed from before to after, that can show effective the fuel polishing service was, instead of leaving it up to assumption.  And if the customer sees a fuel stability test, they have hard evidence that their fuel’s condition changed for the better.

Fuel Stability – What To Do?

Because oxidative stability readings are of a predictive nature, you actually have two kinds of remediation to consider. So your action items for what to do with fuel that appears likely to go unstable in the future are to do two things: 

  1. remove those existing molecular precursors (that the test shows are going to be the elements in the fuel forming heavy end dropout in the near future), and
  2. treat the fuel to prevent future chain reactions leading to formation of insoluble.

For the first part, fuel polishing would remove these larger precursor molecules and any existing insolubles that may have already formed.  This alone can make a significant improvement in the fuel’s stability rating, because fuel without precursor molecules already present will last longer in storage without changing condition.

For the second part, fuel should then be chemically treated, either by independent of, or during, some kind of polishing/filtering service, with a stabilizer to halt further degradation and extend its effective storage life.

Action Items For Entities With Stored Fuel – The Issue of Cost for Testing

Combining these tests with the required ASTM D-975 slate will give stored fuel users like hospitals and health care facilities the best and most accurate picture of their fuel’s condition at any given time.  Given what’s at stake for these facilities, they are well worth considering.

But running a slate of these tests a la carte can cost upwards of $1000+ at an accredited lab. That may be sticker shock for some health care purchasing or operations managers, but may not be all that much when compared to both the costs of damage to large volumes of stored emergency fuel and the tremendous costs of failure should their fuel not perform when called upon to do so.  Not to mention factoring in the additional potential cost incurred if a health care facility cannot provide essential services in an emergency because their stored fuel doesn’t perform as needed, and the perspective on the cost of this kind of testing shifts significantly.

Where to have tests like these done?

There are plenty of testing laboratories available that can do these tests with a pretty quick turnaround. 

Selecting A Partner To Help Get It Done

One option is that stored fuel customers can reduce these costs by partnering with someone who has existing relationships with accredited testing labs - a great way to get these done, but at a fraction of the cost.  For example, Bell Fuel & Tank Services customers who rely on the FTS program for preventive fuel maintenance can have these tests run for a fraction of the cost.   Either way, many times such a partner can not only get the same tests done at a fraction of the normal cost, they can help take care of packaging up the sample, submitting it for testing, apprising you of the results and helping to provide guidance on what the next steps may need to be.


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